VTOL vehicles rely on direct thrust from propellers or rotors arranged to direct air flow downwardly for generating the lift forces necessary to lift the vehicle off the ground and to support the vehicle in a hover mode. Many different types of VTOL vehicles have been proposed where the weight of the vehicle in hover is carried directly by the rotors, with the axes of rotation of the rotors extending vertically, and substantially perpendicular to the ground. Some VTOL vehicles use propellers having their axes of rotation fully rotatable (up to 90° or so) with respect to the body of the vehicle. In vehicles of this kind, the rotors are arranged on wings on opposite sides of the fuselage (such as the V-22 Osprey), or in ducts supported on opposite sides of the fuselage (such as the Moller M400 Skycar), and the axes of rotation of the propellers are oriented substantially perpendicular to the ground for take-off hover and landing, and are tilted forward for normal, forward flight. Other vehicles use propellers having nearly horizontal axes of rotation, but include aerodynamic deflectors installed behind the propellers which deflect all or part of the flow downwardly to create direct upward lift for take-off.
In the Piasecki PA-59 (the “Flying Jeep”), the rearward of two coaxial ducted fans lying on the longitudinal axis of the vehicle, is fixed to the vehicle chassis at an angle relative to the vehicle's longitudinal axis to create both lift and forward thrust components. The forward ducted fan is also fixed to the chassis, but with its axis of rotation substantially perpendicular to the vehicle's longitudinal axis, and thus generating only lift forces while the chassis is horizontal.
In U.S. Pat. No. 5,454,531 (Melkuti), a ducted propeller aircraft is disclosed that includes a primary ducted propeller assembly centered beneath the cockpit, with left and right control ducted propellers in the aircraft wing sections. The ducted propeller assemblies are angularly fixed relative to the aircraft fuselage, i.e., the ducted propeller assemblies are fixed at an angle of about 22° relative to the fuselage in a horizontal orientation. Accordingly, in a horizontal flight mode, the ducted propeller assemblies are deployed at an angle of about 22° to horizontal (and to the incoming air streams), and exiting air is redirected to fully horizontal by a series of louvers to thereby produce forward thrust. For vertical flight, the aircraft fuselage is tilted upwardly such that the ducted propeller assemblies are substantially horizontal, and the louvers are adjusted to produce a substantially vertical thrust component.
In the past, vehicles with wing-supported, tiltable ducted fans, or VTOL vehicles with ducted fans supported directly on either side of the fuselage, have had a distinct disadvantage in terms of establishing a reduced profile or footprint for accessing confined areas. In addition, VTOL vehicles generally have been unable to generate a sufficiently high speed in forward flight for many applications.
There remains a need, therefore, for a VTOL craft or vehicle with a small lateral footprint or profile for accessing closely confined spaces, such as, for example, between tall buildings in a dense, urban environment and that also generates higher speed in forward flight.